Hydrocarbon reservoirs are exploited by drilling wells in a hydrocarbon bearing geologic formation. Producing wells (producers) are drilled to allow hydrocarbons to flow to the surface. The key to efficient recovery of petroleum from a petroleum reservoir is to efficiently design, place, and operate wells. In order to guide and optimize well design, placement, and operation, accurate forecasts of future well behavior are necessary.
A widespread method used to forecast the production behavior of petroleum wells is known as decline-curve analysis (DCA). Decline curve analysis is a type of engineering analysis that uses an analytical functional form, the decline curve, to represent physical well production behavior. The decline curve is based on an integral form of the mass conservation equation enforced on the drainage volume of the well and reformulated to express the variation of the well production rate over time. Three main types of decline curves are used: exponential, parabolic and hyperbolic. Each type is used for a specific type of well. The DCA process remain the same in all cases: the decline curve is fitted through the recent historical behavior of the well production rate and is then used to extrapolate the well behavior forward in time. The predictions obtained through DCA are usually a conservative estimate of the amount of fluids to be produced by a given well.
One of the key difficulties in applying DCA is the complexity of the well production data. To analyze large reservoirs, portfolios of fields, or even entire companies, it is not uncommon that hundreds or even thousands of wells must be measured and analyzed. The production history of each well may contain reporting errors and/or noise. Applying DCA on a field therefore typically requires a significant amount of manpower to review each individual well and identify the best decline curve to represent changes in the physical production of the well. In addition to being a slow and painstaking process, this analysis is also subject to the bias of each analyzing engineer.